This invention concerns methods of preheating fuel injected into the intake manifold or cylinders of automotive engines. Fuel injection occurs when a small diameter needle valve is lifted from a valve seat to allow pressurized fuel to spray out through a valve seat orifice and into the engine where it vaporizes.
It has heretofore been recognized that preheating of the fuel during cold starting will greatly reduce emissions caused by incomplete fuel vaporization during cold starts.
Various heater arrangements have been proposed, including an external heater jacket on the injector body, a heater internally of the injector, such as described in U.S. Pat. Nos. 4,458,655; 3,868,939 and 4,898,142. In the prior upstream heaters, the heater is installed well above the point where injection occurs, such that cooling can occur before injection.
Another approach is a heater element downstream of the valve seat, on which fuel is sprayed when the valve injector opens, such as described in U.S. Pat. Nos. 4,627,405 and 4,572,146.
In this downstream arrangement, the presence of the heater affects the spray pattern, such that the pattern is different when the heater is operated, as may occur with the downstream heaters referenced above. Coking problems also arise where heated surfaces are not continuously wet with fuel, as in these downstream heaters.
An object of the present invention is to provide an improved method for preheating fuel in association with a fuel injector and for establishing reliable electrical connections to an internal heater used to preheat the fuel.